with their magic: Heb. בְּלַהִטֵיהֶם [Onkelos renders בְּלַחֲשֵהון], [meaning] with their incantations. It [the word בְּלַהִטֵיהֶם has no similarity in the [rest of] Scripture. It may, however, be compared to “the blade of (לַהַט) the revolving sword” (Gen. 3:24), which seemed to be revolving because of a magic spell.

is heavy: Heb. כָּבֵד. Its Aramaic translation is יַקִיר [heavy], and not אִתְיַקַר [has become heavy], because it is the name of a thing [an adjective and not a verb], as in for the matter is too heavy (כָבֵד) for you (Exod. 18:18).

15Go to Pharaoh in the morning; behold, he is going forth to the water, and you shall stand opposite him on the bank of the Nile, and the staff that was turned into a serpent you shall take in your hand.

behold, he is going forth to the water: to relieve himself, for he had deified himself and said that he did not need to relieve himself; so, early in the morning he went out to the Nile and there he would perform his needs. — [from Mid. Tanchuma, Va’era 14; Exod. Rabbah 9:8]

until now: Heb. עַד-כֹּה, [meaning] until now [Onkelos]. Its midrashic interpretation is: Until you hear from me [the announcement of] the plague of the firstborn, which I will introduce with “So (כֹּה said the Lord, ‘When the night divides…’” (Exod. 11: 4). — [from an unknown midrashic source]

and it will turn to blood: Since there is no rainfall in Egypt, and the Nile ascends and waters the land, so the Egyptians worship the Nile. He therefore smote their deity and afterwards He smote them. — [from Sifrei, Devarim 38; Exod. Rabbah 9:9; Tanchuma, Va’era 13]

and the Egyptians will weary: Heb. וְנִלְאוּ [I.e., the Egyptians will become weary trying] to seek a remedy for the waters of the Nile so that it would be fit to drink. — [from Jonathan]

ונלאו מצרים: לבקש רפואה למי היאור שיהיו ראוין לשתות:

19The Lord said to Moses, "Say to Aaron, 'Take your staff and stretch forth your hand over the waters of Egypt, over their rivers, over their canals, over their ponds, and over all their bodies of water, and they will become blood, and there will be blood throughout the entire land of Egypt, even in wood and in stone.' "

their canals: Heb. יְאֹרֵיהֶם. These are man-made pools and ditches, [extending] from the riverbank to the fields. [When] the waters of the Nile increase, it [the Nile] rises through the canals and irrigates the fields. — [from Othioth d’Rabbi Akiva

throughout the entire land of Egypt: Even in the bathhouses, and in the bathtubs in the houses.

בכל ארץ מצרים: אף במרחצאות ובאמבטאות שבבתים:

even in wood and in stone: Water in wooden vessels and in stone vessels. — [from Onkelos, Jonathan, Exod. Rabbah 9:11]

ובעצים ובאבנים: מים שבכלי עץ ובכלי אבן:

20Moses and Aaron did so, as the Lord had commanded, and he raised the staff and struck the water that was in the Nile before the eyes of Pharaoh and before the eyes of his servants, and all the water that was in the Nile turned to blood.

and Pharaoh’s heart was steadfast: saying, “You are doing this through sorcery. ‘You are bringing straw to Aphraim,’ a city that is full of straw. So too you bring magic to Egypt, which is [already] full of magic.” - from Exod. Rabbah 9:11, Men. 85a]

Seven full days passed: Heb. וַיְּמָּלֵא, literally, seven days were filled. Since the word וַיְּמָּלֵא is singular, Rashi explains: The number of seven days that the Nile did not return to its original state [was filled], for the plague would be in effect for a quarter of a month, and for three quarters [of the month], he [Moses] would exhort and warn them. — [from Tanchuma, Va’era 13, Exod. Rabbah 9:12, as explained by Mizrachi and Gur Aryeh].

But if you refuse: Heb. מָאֵן, [which means] and if you are a refuser. מָאֵן is like מְמָאֵן, refuses, but Scripture calls the person by his action, like “tranquil (שָׁלֵו) and still (וְשָׁקֵט) ” (see Job 16:12) 4; “sad and upset (וְזָעֵף)” (I Kings 20:43).

28And the Nile will swarm with frogs, and they will go up and come into your house and into your bedroom and upon your bed and into the house of your servants and into your people, and into your ovens and into your kneading troughs;

into your house: and afterwards, into the house of your servants. He [Pharaoh] introduced the plan first, [as it is written:] “He said to his people…” (Exod. 1:9), and with him the retribution started. — [from Sotah 11a]

and the frogs came up: Heb. וַתַּעַל הַצְפַרְדֵעַ, literally, and the frog came up. It was one frog, and they [the Egyptians] hit it, and it split into many swarms of frogs. This is its midrashic interpretation (Tanchuma, Va’era 14); for its simple meaning, it can be said that the swarming of the frogs is referred to as singular, and likewise, “and the lice were (וַתְּהִי הַכִּנָם) ” (verse 13), the swarming, pedoiliyere in Old French, swarming of lice, and also וַתַּעַל הַצְּפַרְדֵּע, grenoylede in Old French, swarming of frogs.

4Thereupon, Pharaoh summoned Moses and Aaron, and said, "Entreat the Lord that He remove the frogs from me and from my people, and I will let out the people [of Israel] so that they may sacrifice to the Lord."

5And Moses said to Pharaoh, "Boast [of your superiority] over me. For when shall I entreat for you, for your servants, and for your people, to destroy the frogs from you and from your houses, [that] they should remain only in the Nile? "

Boast [of your superiority] over me: Heb. הִתְפָּאֵר עָלַי, similar to “Shall the axe boast (הִיִתְפָּאֵר) over the one who hews with it” (Isa. 10:15). It praises itself, saying, “I am greater than you,” vanter in Old French. Similarly, הִתְפָּאֵר עָלַי, [Moses says to Pharaoh,] “you praise yourself by acting cleverly and asking a difficult thing and saying that I will be unable to do it.”

For when shall I entreat for you: Heb. לְמָתַי. That which I will entreat for you today regarding the extermination of the frogs [tell me,] when do you wish them to be exterminated? And you will see whether I fulfill my words for the time that you set for me. If it were stated, מָתַי אַעְתִּיר it would mean “When shall I pray?” Now that it says, לְמָתַי [and thus it means:] Today I will pray for you that the frogs will be exterminated at the time that you set for me. Tell me, on which day do you want them to be exterminated? [The Torah uses three words:] אַעְתִּיר, I will entreat; הַעְתִּירוּ ((verse 4), entreat (command form); וְהַעְתַּרְתִּי (verse 25), and I will entreat [all in the “hiph’il,” causative conjugation], and it does not say, אֶעְתַּר, עִתְרוּ, and וְעָתַרְתִּי [in the “kal,” simple conjugation], because every expression of עתר means to pray very much, and just as one says אַרְבֶּה, I will increase, הַרְבּוּ, increase [command form], וְהִרְבֵּיתִי, and I will increase, in the “hiph’il” conjugation, so does one say: אַעְתִּיר, I will increase, הַעְךְתִּירוּ (verse 4), increase [command form] וְהַעְתַּרְתִּי (verse 25), and I will increase words, and the “father” [i.e., the main proof] of them all is: “ הַעְתַּרְתֶּם your words” (Ezek. 35:13), you have multiplied.